Control method of tension in rolling mills (1)

ABSTRACT

In a cold tandem mill of the endless type, means are provided to maintain the strip tension constant while the cross-section of the strip undergoes a change in size, that is, as the thickness, the width or the desired finished thickness of the strip is changed.

United States Patent 1 1 1111 3,760,621 Fujii et al. 7 1451 Sept. 25, 1973 CONTROL METHOD OF TENSION IN ROLLING MILLS (1) [56] References Cited [75] Inventors: Seiii Fujii; Hiroshi Kuwamoto; UNITED STATES PATENTS Mammoto Kamata; Masayoki 3,603,124 9/1971 Arimura et al. 72/8 Ishida, all of Fukuyama, Japan 3,618,348 11/ 1971 Arimura et al. 72/7 [73] Assignee: Nippon Kokan Kabushiki Kaisha, ck y Japan [22] Filed: Aug. 20, 1971 Primary ExaminerMiIton S. Mehr [21] pp No: 176,766 AttorneyRobert D. Flynn et al.

30 F A D [57] ABSTRACT 1 orelgn pphcatmn Pnomy am In a cold tandem mill of the endless type, means are Aug. 26, I970 Japan 45/74281 provided to maintain the strip tension constant while the cross-section of the strip undergoes a change in E2 size, that is, as the thickness, the width or the desired ll. fth h 581 Field oiSearch., 72/8, 9, 10, 11, 6 0 e S ange 72/12 1 19 10 Claims, 4 Drawing Figures THICKNESS SIGNAL WIDTI-I S IGNAL 4 MULTIPLIEIZ-- CROSS-SECTIONAL IO AREA SIGNAL.\

TENSILE MULTIPLIER XHSTRESS 14.1), II SETTING TOTAL TENSION STAND MEASURED TOTAL. J, SIGNAL 5 6 VTENYSIOVNYI SIGNAL SUMMING POINT TENSION CONTROLLER- DEVIATION SIGNAL PAIENIED 3.760.621

sum 1 nr 2 THICKNESS SIGNAL WIDTH SIGNAL cRoss-ssc'nom. AREA SIGNAL Ii-I-IIII'] SETTING STAND TOTAL TENSION MEASUREO TOTAL- SIGNAL 5 6 TENSION SIGNAL. SUMMNG POINT TENSION CONTROLLER E N SIGNAL lz THICKNESS SIGNAL. 3

l 2 l DELAY f WIDTH SIGNAL CROSS SECTIONAI- MUL'I'IILIEIZ X AREA SIGNAL MULTIPLIEP T N h X S v STAN SETTING TOTAL TENSION Q 7 TENSION SIGNAL SUMMING POINT CONTROLLER DEVIATION SIGNAL PATENTEUSEPZSW 3.760.621

' sum 2 or 2 SLAMMING POINT F] G 3 EW DOWN POSITION $l6NAL THICKNESS SIGNAL.

aoume LOAD sIGNAL f LAM-19 WIDTH 5&6NAL

18 0: MULTIPLIER CR53 l0 ssc-norum. v g MULTiPLlER AREA mm a T N STANDQ) 8 GEM I STAND I TOTAL MEASURED TOTAL TENSON 6 g 'f T NSION S16NAI.

' CONTROLLER suMMme POINT DEVIATJON smmm.

FIG. 4 THICKNESS swNAL WIDTH SlGNAL SIGNAL m MEASURED TOTAL TENSI TENSION/ TENSION sncmm. CONTROLLER summme POINT Iz DEVlATlON SIGNAL CONTROL METHOD OF TENSION IN ROLLING MILLS (1) In large scale cold tandem mills, it is the recent trend that bigger and longer coils are used and further, that the material strips supplied to the rolls are welded preliminarily so that the strips will be in an endless form. Under these circumstances, it has become necessary to conduct a speedy and automatic control of the strip tension between the stands of such cold tandem roll trains so that products of different shapes may be obtained from one endless rolling operation.

The present invention is directed to a control method for maintaining a constant tension per cross sectional area of a strip (referred to as constant tensile stress) during the rolling process even when the plate thickness and/or width is changed during rolling of strips.

As the art of changing the strip thickness during rolling is an entirely new art, there is naturally no prior method of control to handle the present problem. However, there has been up to new methods such as detecting the strip tension with a tension meter, controlling the roll gaps or the roll speed in the succeeding and preceding stands, and maintaining the tension at a constant value. However, the tension measured by the tension meter is the total tension of the strip, whereas the aimed at value which needs control during rolling the strip thickness and the width.

is the tension per cross sectional area (hereinafter referred to as tensile stress). In a batch typerolling mill where one length of strip is rolled in one operation, there is no need to change the plate thickness during rolling. Therefore, calculation of a desired value for the total tension prior to the start of the rolling operation by multiplying the desired tensile stress by the strip thickness and the width will eliminate the need to change the value during rolling. In an endless type rolling mills wherein the thickness and/or width of the material strip or the aimed" thickness is changed during rolling, the prior art type of constant control on the total tension will cause such defects as the tensile stress will be different from the aimed or desired value at the point that the thickness and/or width of the strip is changed. I

In order to obviate such defects, it is possible to time the change of the strip thickness and/or width with the change of the aimed total tension value. However, the tensile strength tends to become transitionally abnormal whensuch timing is not conducted properly.

In view of the foregoing, there has been a strong demand in the art for development of a control method that will automatically change the aimed value of the total tension corresponding to the change in the strip thickness during the rolling operation.

The total tension of the strip is obtained, generally, by multiplying the tensile stress by the plate thickness and by the width:

wherein T stands for total tension, 1 fortensile stress, h for strip thickness and w for strip width.

SUMMARY OF THE INVENTION The present invention aims at a constant control of the tensile stress by automatically measuring the strip thickness and the strip width by measuring devices and by automatically changing the aimed value of the total Thepresent invention will now be described more in detail, references being made to the accompanying drawings wherein FIGS. 1 to 4 show block diagrams of preferred embodiments of tension control in accordance with the present invention.

More in detail, FIG. 1 is a block diagram showing one embodiment of the constant control system for use in a tandem cold rolling mill having a plurality of stands. Between the (i)th stand and the (i-i-l )th stand in such a tandem mill, there is conducted an operation to obtain an aimed value. In the FIG. 1, (1) denotes the (i)th stand rolling machine, (2) the (i+l )th stand rolling machine, (3) and (4) the electric motors for each stand for screw down purposes, (5) and (6) the electric motors for driving purposes for each stand, (7) the thickness detector, (8) a width detector, (9) a tension meter, (10) and (11) the multiplying calculators, and (12) a tension control circuit. The thickness and the width of the strip being rolled are detected by the thickness detector (7) and the width detector (8) and placed in the multiplier (10). In the multiplier (10), the values of thickness signal and the width signal are multiplied and the output signal represents the cross sectional area of the strip. Further in the multiplier (11), the value of the cross sectional area signal from the multiplier (10) is multiplied by the tensile stress obtained by preliminary manual calculation, and the output signal of multiplifer (11) is the total tension required to get the desired value of tensile stress in the strip. The value of the tension signal detected by the tension meter (9) on the other hand is compared with the value of the output signal delivered from the multiplier (11) which is the aimed value of the tension and the difference therebetween is fed into the constant control circuit (12) as a deviation. A conventional type tension control method or a limited tension control method maybe used for the constant control circuit (12) of this invention. That is, when the tension becomes more than the aimed or desired value, the screw downofthe succeeding stand ((i-l-l )th stand in this instance) is screwed down, or the roll speed of the preceding stand ((i)th stand in this instance.) is incremented. If the tension becomes smaller than the aimed or desired value, then the screw down of the succeeding stand is screwed up, or the roll speed of the preceding stand is decremented.

FIG. 2 shows an improvement over the embodiment of FIG. 1 in some parts thereof. The embodiment shown in FIG. 2 is the embodiment shown in FIG. 1 to which has been added delay circuits (l3) and (14). The thickness detector (7), the width detector (8) and the tension meter (9) should be at the same location because of the particular nature of this control. However, since it is practically impossible to provide these devices at one place so that the delay circuits (13) and (14) are inserted into the signal lines of the thickness signal and the width signal so as to delay the thickness signal for the period of time that it takes for the strip to run from the point where the thickness detector (7) is to the point where the tension meter (9) is, and also to delay the width signal for the period of time it takes for the strip to run from the width detector (8) to the tension detector (9). Thus, the effect obtained is the same as in the case when the thickness detector, the width detector and the tension meter were located at one place. In this method, the delay circuit will be required in order to vary the delay time proportionate to the rolling speed. Such delay circuit to be used in this invention may be those previously developed in the art. The identical reference numerals in FIG. 2 denote the corresponding parts in FIG. I.

In FIG. 3, a third embodiment of the present invention is shown in which the thickness signal is obtained from the position of the screw down and the rolling load by applying the formula (2) without using the thickness detector for measuring the thickness.

h=S+P/M...

wherein S stands for the position of the screw, P for rolling load, h for strip thickness and M for Mill constant. More in detail, (12) denotes a load cell for measuring rolling load, (14) a screw position detector for detecting the position of the screw and (19) is a device to divide the values from the load cell by Mill constant (hereinafter referred to as a damping device). In the example, the signal from the load cell (17 is converted to the signal corresponding to elongation" of the mill stand by the damping device (19) and then combined with the signal from the screw position detector 18 for screw position detection, which is utilized as the strip thickness signal. The rest of the circuit is the same as the previously described embodiment of the present invention. Although in some rolling schedules wherein the change is made without interruption when the change of width in one instance is small, it is possible to manually give the width signal and to eliminate provision of the width detector. The identical reference numerals in FIG. 3 denote the corresponding parts in FIG. 1.

The deviation fed into the tension control circuit (12) in the above going was the difference between the aimed value and the actual value of the total tension. In the embodiment shown in FIG. 4, the deviation of the tensile stress is fed into the tension control circuit. The signal representing the cross sectional area which is the output of the multiplier and the output signal from the tension meter (9) are fed into the divider to obtain the tensile stress: i.e., the total tension is divided by the cross sectional area. This tensile stress thus obtained is compared with the aimed tensile stress and the difference therebetween is fed into the tension controller 12.

In accordance with the present invention, it is possible to maintain the tensile stress of the strip at a desired constant value even when the material thickness and/or width, and/or the finished thickness of the strip is changed even during the transitory period during such change. This enables the prevention of strip ruptures and facilitates smooth operation of the size alteration in the rolling operation of the strip rolling mill.

What is claimed is:

1. In cold tandem rolling of a continuous strip comprised of metal strips of varying sizes which are welded together, a method of control to maintain the tensile stress of said continuous strip'constant even with varying width of the continuous strip, comprising:

detecting, during the rolling operation, a changed cross-section of said continuous strip downstream of a given welded point and adjacent said given welded point due to a change of the width of the strip being rolled at said welded point;

generating signals which are a function of said changed width and of the desired tensile stress in the strip after said change in said width; and

controlling the rolling operation as a function of said generated signals to maintain said tensile stress of said strip constant.

2. The method according to claim 1 wherein said detecting step includes measuring the size of the strip downstream of the change in width thereof, calculating the cross-section of the strip as a function of said measured size, and wherein said generating step includes multiplying the calculated cross-section by the desired tensile stress to obtain the total desired tension, measuring total tension in the strip downstream of the change in width thereof, comparing the said desired total tension with measured total tension and generating control signals as a function of said comparison, said control signals being used in controlling the rolling operation to maintain said tensile stress constant.

3. The method according to claim 1 wherein said detecting step includes measuring the cross-sectional area of the strip downstream of the change in width thereof, and wherein said generating step includes measuring total tension in the strip downstream of the change in width thereof, dividing measured total tension by measured cross-sectional area to obtain tensile stress, comparing the measured tensile stress with desired tensile stress and generating control signals as a function of said comparison, said control signals being used in controlling the rolling operation to maintain said tensile stress constant.

4. The method according to claim 1 wherein said detecting step includes measuring the thickness of the strip downstream of the change in width thereof during rolling and generating a signal corresponding to the measured thickness; measuring the changed width of the strip during rolling and generating a signal corresponding to said width; multiplying the thickness signal and the width signal to generate a signal corresponding to the cross-sectional area of the strip; and wherein said generating step includes multiplying the measured cross-sectional area signal by a predetermined signal representing desired tensile stress in the strip to obtain a signal corresponding to desired total tension in the strip; measuring the total tension in the strip downstream of the change in width thereof during rolling and generating a signal corresponding to the measured total tension; and comparing the measured total tension signal with the total desired tension signal derived from the predetermined desired tensile stress to generate a deviation signal; said deviation signal being used in controlling the rolling operation to maintain said tensile stress constant and at a predetermined value.

5. The method according to claim 1 wherein saiddetecting step includes measuring at least the width of the strip downstream of the change in width thereof during rolling; determining the cross-sectional area of the strip from the measured width and generating a signal corresponding to the cross-sectional area; and wherein said generating step includes generating a total desired tension signal from the cross-sectional area signal.

6. The method according to claim 5 further comprising measuring the thickness of said strip downstream of the change in width thereof during rolling and using the measured thickness to determine cross-sectional area of the strip.

7. The method according to claim 6 wherein said thickness and width of said strip are measured at different points in the direction of travel of said strip, and including the step of delaying the signal corresponding to at least one of the measurements such that the signals corresponding to both of said measurements coincide with each other in time.

8. The method according to claim 6 wherein said thickness is measured by generating a signal corresponding to the screw down position of a set of rolls; generating a signal corresponding to the rolling load of the same set of rolls; and summing said rolling load and screw down position signals to and from a signal representing a predetermined desired tensile stress in the strip; and comparing the total desired tension signal with another signal representing measured total tension in the strip downstream of the change in width thereof to generate a deviation signal; said deviation signal being used in controlling the rolling operation to maintain said tensile stress constant at a predetermined value.

9. The method according to claim 1 wherein said dey during rolling and generating a signal corresponding to said measured width; determining the cross-sectional area from said measured width signal and generating a cross-sectional area signal; and wherein said generating step includes measuring the total tension in said strip downstream of the change in width thereof during rolling and generating a measured total tension signal; dividing said cross-sectional area signal by said measured total tension signal to generate a tensile stress signal; and comparing said tensile stress signal with a predetermined tensile stress setting which corresponds to a predetermined desired tensile stress in said strip and generating a deviation signal, said deviation signal being used in controlling the rolling operation to maintain said tensile stress constant and at a predetermined value.

10. The method according to claim 9 wherein said detecting step includes measuring the thickness of said strip downstream of the change in width thereof and generating a signal corresponding to the measured thickness, and wherein said step of generating a crosssectional area signal comprises multiplying the measured thickness signal with the measured width signal.

Patent No. 3,760,621

Dated September 25, 1973 Inventor(s) ji FUJII et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE CLAIMS: Column4, line 62, after farea signal" insert '-'-and from a signal representing a predetermined desired tensile stress in the strip; and comparing the total desired tension signal with' another signal representing measured total tension in the strip downstream of the change in width thereof to generate a deviation signal; said deviation signal being used. in controlling the rolling operation to maintain said tensile stress constant at a predetermined value';

Column 5, line 13, after "position signals to"-del ete "andvfrom a signal repre" and insert -generate a'signal corresponding to the thickness of the strip being rolled.;

delete .lines 14-21 IORM PC4050 USCOMM-DC wan-Poo fi U.S. GOVERNMENT PRINTING OFFICE l9! 6-3l-334.

UNITED STATES PATENT OFFICE Page 2 RTIFICATE OF CORRECTION Patent No. 3,760,621 Dated September 25, 1973 Inventor(s) Seiji FUJII et al It is certified that error appears in the above-identified patent V and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, change fourth inventors first name to -'-'-Masayuki.

Signed and sealed this 5th day of March 197Lt.

(SEAL) Attest: I

EDI/JARD M.FLETC HER,JR. Y A HALLDANN At te ti Qffi'de I Commissioner of Patents ORM F'O-1050 (10-69) USCOMM-DC wan-ps9 a USt GOVERNMENT PRINTING OFFICE 5 ID" 36 -33l, 

1. In cold tandem rolling of a continuous strip comprised of metal strips of varying sizes which are welded together, a method of control to maintain the tensile stress of said continuous strip constant even with varying width of the continuous strip, comprising: detecting, during the rolling operation, a changed cross-section of said continuous strip downstream of a given welded point and adjacent said given welded point due to a change of the width of the strip being rolled at said welded point; generating signals which are a function of said changed width and of the desired tensile stress in the strip after said change in said width; and controlling the rolling operation as a function of said generated signals to maintain said tensile stress of said strip constant.
 2. The method according to claim 1 wherein said detecting step includes measuring the size of the strip downstream of the change in width thereof, calculating the cross-section of the strip as a function of said measured size, and wherein said generating step includes multiplying the calculated cross-section by the desired tensile stress to obtain the total desired tension, measuring total tension in the strip downstream of the change in width thereof, coMparing the said desired total tension with measured total tension and generating control signals as a function of said comparison, said control signals being used in controlling the rolling operation to maintain said tensile stress constant.
 3. The method according to claim 1 wherein said detecting step includes measuring the cross-sectional area of the strip downstream of the change in width thereof, and wherein said generating step includes measuring total tension in the strip downstream of the change in width thereof, dividing measured total tension by measured cross-sectional area to obtain tensile stress, comparing the measured tensile stress with desired tensile stress and generating control signals as a function of said comparison, said control signals being used in controlling the rolling operation to maintain said tensile stress constant.
 4. The method according to claim 1 wherein said detecting step includes measuring the thickness of the strip downstream of the change in width thereof during rolling and generating a signal corresponding to the measured thickness; measuring the changed width of the strip during rolling and generating a signal corresponding to said width; multiplying the thickness signal and the width signal to generate a signal corresponding to the cross-sectional area of the strip; and wherein said generating step includes multiplying the measured cross-sectional area signal by a predetermined signal representing desired tensile stress in the strip to obtain a signal corresponding to desired total tension in the strip; measuring the total tension in the strip downstream of the change in width thereof during rolling and generating a signal corresponding to the measured total tension; and comparing the measured total tension signal with the total desired tension signal derived from the predetermined desired tensile stress to generate a deviation signal; said deviation signal being used in controlling the rolling operation to maintain said tensile stress constant and at a predetermined value.
 5. The method according to claim 1 wherein said detecting step includes measuring at least the width of the strip downstream of the change in width thereof during rolling; determining the cross-sectional area of the strip from the measured width and generating a signal corresponding to the cross-sectional area; and wherein said generating step includes generating a total desired tension signal from the cross-sectional area signal.
 6. The method according to claim 5 further comprising measuring the thickness of said strip downstream of the change in width thereof during rolling and using the measured thickness to determine cross-sectional area of the strip.
 7. The method according to claim 6 wherein said thickness and width of said strip are measured at different points in the direction of travel of said strip, and including the step of delaying the signal corresponding to at least one of the measurements such that the signals corresponding to both of said measurements coincide with each other in time.
 8. The method according to claim 6 wherein said thickness is measured by generating a signal corresponding to the screw down position of a set of rolls; generating a signal corresponding to the rolling load of the same set of rolls; and summing said rolling load and screw down position signals to and from a signal representing a predetermined desired tensile stress in the strip; and comparing the total desired tension signal with another signal representing measured total tension in the strip downstream of the change in width thereof to generate a deviation signal; said deviation signal being used in controlling the rolling operation to maintain said tensile stress constant at a predetermined value.
 9. The method according to claim 1 wherein said detecting step comprises measuring at least the width of the strip downstream of the change in width thereof during rolling and generating a signal corresponding to said measured width; determinIng the cross-sectional area from said measured width signal and generating a cross-sectional area signal; and wherein said generating step includes measuring the total tension in said strip downstream of the change in width thereof during rolling and generating a measured total tension signal; dividing said cross-sectional area signal by said measured total tension signal to generate a tensile stress signal; and comparing said tensile stress signal with a predetermined tensile stress setting which corresponds to a predetermined desired tensile stress in said strip and generating a deviation signal, said deviation signal being used in controlling the rolling operation to maintain said tensile stress constant and at a predetermined value.
 10. The method according to claim 9 wherein said detecting step includes measuring the thickness of said strip downstream of the change in width thereof and generating a signal corresponding to the measured thickness, and wherein said step of generating a cross-sectional area signal comprises multiplying the measured thickness signal with the measured width signal. 